I am interested in a term that occurs in the Rinzai Roku; I think the Japanese is something like rei on, translated as "wondrous voice" in the Sasaki/Kirchner edition (p.252). Has anyone heard a teacher expound upon the meaning of this in teisho, or have scholars had anything to say? What do the ideographs mean literally?

The term lingyin 靈音 seems particular to the Linjilu, so here ling 靈 is a qualifier for yin 音, thus the translation "wondrous voice" (Sasaki) or "miraculous sound" (Watson). Ling 靈 has a good number of meanings, and can be a member of various compounds.

In the teaching hall the master said, "The spiritual light (靈光) shines alone, far transcending the senses and their fields; the essential substance is exposed, real and eternal. It is not contained in written words. The nature of mind has no defilement; it is basically perfect and complete in itself. Just get rid of delusive attachments, and merge with realization of thusness."

From Jinul (Collected Works of Korean Buddhism, vol 2, p 129):

"When falsity is extinguished, the mind will be numinous and dynamic (靈通); then the effulgence of superpowers will appear in response."

He also quotes Zongmi (p 214):

"When delusion is extinguished, the mind will become numinous and dynamic (靈通) and, in response, will make manifest its function of penetrating illumination."

Another compound often used by Jinul (p 219):

"Since all dharmas are like dreams or conjuring tricks, deluded thoughts are originally calm and the dusty sense-spheres are originally empty. At the point where all dharmas are empty, the numinous awareness is unobscured. That is, this mind of void and calm, numinous awareness (靈知) is your original face"

Now if we turn to Linji, the use of ling 靈 is mainly for the vividness of apparent experiences (tr Sasaki, p 240):

"The three realms do not of themselves proclaim: ‘We are the three realms!’ But you, followers of the Way, right now vividly (目前靈靈) illumining all things and taking the measure of the world, you give the names to the three realms."

(p 273):

"Moreover, names and phrases are not of themselves names and phrases; it is you, who right now radiantly and vividly (目前昭昭靈靈) perceive, know, and clearly illumine [everything]—you it is who affix all names and phrases."

To connect the two meaning of vividness and wondrous, it means the unabiding perception (e.g. of sound 聲, p 227):

"Those are not the six supernatural powers of a buddha, which are entering the world of color yet not being deluded by color; entering the world of sound yet not being deluded by sound; entering the world of odor yet not being deluded by odor; entering the world of taste yet not being deluded by taste; entering the world of touch yet not being deluded by touch; entering the world of dharmas yet not being deluded by dharmas. Therefore, when it is realized that these six—color, sound, odor, taste, touch, and dharmas— are all empty forms, they cannot bind the man of the Way, dependent upon nothing."

And comparing to an echo (p 275):

"When the place of arising or extinguishing of a single thought in your mind is not to be found, as with a sound reverberating throughout space (響應空), and there is nothing anywhere for you to do"

Finally, the original sentence to be considered (p 252):

"if you don’t seek him, then he’s right there before your eyes, his wondrous voice (靈音) resounding in your ears."

We can say that his voice being wondrous stands for hearing without attachment.

1Myriad dharmas are only mind.
Mind is unobtainable.
What is there to seek?2If the Buddha-Nature is seen,
there will be no seeing of a nature in any thing.3Neither cultivation nor seated meditation —
this is the pure Chan of Tathagata.4With sudden enlightenment to Tathagata Chan,
the six paramitas and myriad means
are complete within that essence.